Two of the unsolved problems in the field of automatic dishwashing are those of cleaning tough food residues and of preventing filming and spotting of washed articles, especially glass and plastic articles. Filming and spotting are believed to occur, among other reasons, due to the formation of insoluble salts resulting from the combination between the ions generated from the dishwashing detergent and the ions present in the dishwasher water. Food soils also play a significant role in causing filming and spotting. Traditionally, this problem has been ameliorated by the use of salt in order to soften the water (that is to reduce the concentration of cations, specially Ca2+ and Mg2+) and by the use of rinse aid containing sequestrant, dispersant and surfactant which to some extent help to control the hardness of the ions present in the water and to reduce the surface tension of the dishwashing liquor, thus avoiding the formation of liquid droplets and allowing uniform drying of the washed utensils, ameliorating filming and spotting issues.
However, some consumers do not use salt or rinse aid or the water is so hard that salt and rinse aid are not enough to overcome filming and spotting problems. Moreover, the problem of food soils and removal of tough food residues still remains a significant issue.
Typically, the machine dishwashing process involves the steps of dosing detergent into the dispenser at the beginning of each wash and filling the salt and rinse aid reservoirs at intervals as required. Some users may find it inconvenient to carry out all these steps and prefer a simpler process involving the use of a single product performing all the functions required for the dishwashing process. Unitised doses of dishwashing detergents are found to be more attractive and convenient to some consumers, additionally they avoid the need of the consumer to measure the product thereby giving rise to a more precise dosing and avoiding wasteful overdosing or underdosing. For this reason automatic dishwashing detergent products in tablet form have become very popular. Detergent products in pouch form are also known in the art.
Rinse aid compositions need to be stored in the rinse reservoir inside the dishwasher, usually during many cycles and therefore subject to the temperature changes associated with the dishwashing process. Thus rinse aid compositions need to be very stable in order to withstand these temperature changes without affecting their physical form and/or chemical structure. This usually requires the use of very dilute compositions, which limits even further the amount of actives that can be delivered into the rinse cycle.
Some attempts have been made to provide controlled delivery of rinse aid. For example WO-A-00/6684 and WO-A-00/6688 describe a multi-phase tablet comprising a particle which comprises a core and a coating. The substances present in the core are active during the rinse cycle and the coating comprises at least one compound whose solubility increases with a declining concentration of a specific ion in the surrounding medium. WO-A-99/27067 describe a multi-phase tablet with a compressed and non-compressed portion where the non-compressed portion does not dissolve until the rinse cycle. EP-A-851,024 describes a multi-layer tablet, having a first layer for delivery into the main-wash and a second layer comprising a substance which has a melting point between 55° C. and 70° C. and which is substantially delivery into the rinse cycle. However, the tablets described in WO '84, WO '88, WO '67 and EP '24 only deliver actives into one of the rinses cycles and are not capable of selectively delivering different compositions into different rinse cycles.
U.S. Pat. No. 5,453,216 describes the delivery of actives in the rinse cycle by means of coated particles. The particles, which are introduced into the pre-wash and into main-wash cycles, comprise a core comprising an inorganic builder salt and a waxy coating having a melting point above 65° C. Particles are said to have a diameter from about 1 to about 2.5 mm. As such, it seems likely that a large proportion of the particles will be flushed away with the main wash liquor at the end of the main wash cycle.
WO 01/96514 relates to a mechanical dishwashing composition comprising an anti-scaling polymer and a vehicle releasing at least an effective amount of the polymer into a penultimate and/or final rinse of a dishwashing cycle.
Some detergent ingredients used in dishwashing detergent compositions are liquids. These liquid ingredients can be difficult or costly to include in a solid detergent composition. Also, certain ingredients are preferably transported and supplied to detergent manufacturers in a liquid form and require additional, and sometimes costly, process steps to enable them to be included in a solid detergent composition. An example of these detergent ingredients are surfactants, especially nonionic surfactants which are typically liquid at room temperature or are typically transported and supplied to detergent manufacturers in liquid form. Another example are organic solvents. It would be advantageous to have a detergent composition which allows the different ingredients to be in their natural state i.e., liquid or solid.
The majority of automatic dishwashers have wash programs which last at least one hour but only a relatively small proportion of the total wash program is devoted to active detersive cleaning (i.e. the main-wash cycle, which lasts for about 20 min, and possibly the pre-wash) and only a relative small portion of the final rinse cycle (determined by the dishwasher design) is devoted to chemical finishing. These times do not seem to be sufficient for achieving a satisfactory removal of tough food residues and preventing filming and spotting, however delivery programs are fixed parameters determined by dishwashing machine manufacturers and the user has no control over them.
In view of the above there is still a need for improving tough food cleaning whilst reducing filming and spotting, especially in those instances where users wish to avoid or limit the use of salt and/or rinse aid and in the case of dishwashing under hard water conditions.